In the wake of the '7/7' London bombings many Muslims from the East End helped the victims, appalled at the damage to innocent lives.

Just over a century ago, a young, stranded American sailor stepped out into the foul east London air:

“The region my hansom was now penetrating was one unending slum. The streets were filled with a new and different race of people, short of stature and of wretched or beer-sodden appearance. We rolled along through miles of brick and squalor, and from each cross street and alley flashed long vistas of brick and misery. Here and there lurched a drunken man or woman, and the air was obscene with the sounds of jangling and squabbling.”

Those streets are now strangely quiet. The world the 26-year-old Jack London described in his devastating The People of the Abyss seems to have long-disappeared.

On the wide, Roman-straight expanse of Whitechapel Road, Amharic, Arabic and Bangla jostle for attention with English, Russian and a dozen other tongues. But the young girls with makeup and hijab are nowhere to be seen. The women's entrance to the Jamme Masjid on Brick Lane is closed, for "security reasons". It is one of the few buildings outside the Holy Land to have housed all three religions, and where as a synagogue Jewish anarchists once pelted ultra-Orthodox worshippers with bacon sandwiches on Yom Kippur, the Day of Atonement, in 1907.

"The worshippers fought back and Brick Lane soon became a battleground, with fists and lumps of bacon sandwich flying amid the cashmere coats, shtreimel hats and ringlets," writes author Ed Glinert in his book, East End Chronicles.

The Cockney pubs are locked worlds with sullen, white faces. Only the traditional sweetshops remain busy, young men crowding to buy ladoo, jellaby or perhaps dates imported from the Gulf.

This is 'Banglatown', the heart of London's East End. Long known for its Cockneys, Blitz spirit, Jack the Ripper and notorious gangsters, the Kray Twins, the beat of that heart today lies in the people of a hundred nations; its rhythm the call to prayer, mixing with the rough hip-hop of sound systems.

The area was rebranded by London Mayor Ken Livingstone in homage to its large Bangladeshi immigrant population and the curry houses crowding the famous Brick Lane. It is a place where worlds collide, with the power of 'The City' on its very doorstep and the shame of Bangladeshi prostitutes on its streets.

As dusk draws down, the streets and alleys around Banglatown's imposing East London Mosque – one of Britain's oldest, founded in 1910 – swarm with the faithful. Arab, Bangladeshi, African and converts flow like a river into the great building, squatting on Whitechapel Road, the physical and spiritual centre of this community. Behind it the old Fieldgate Street Great Synagogue is almost lost, swallowed by the rising concrete of the newly-constructed London Muslim Centre (LMC) – housing Muslim businesses, shops, a school, library and gym. I had watched as 15,000 of the faithful had prayed on the roads outside when it opened, crying "Allah Akbar!" to the words of the imam of the ka'abah. It seems a mirror, almost, to the glittering shape of Sir Norman Foster's 'Gherkin' [skyscraper] looming in the near-distance.

It is just a few weeks since the first of the London terror bombings, when 52 were killed and more than 700 wounded by angry young British Muslims, harbouring a twisted Salafi dream.

During that balmy morning – "7/7" as it is already known – the East End was itself a target. Members of the Mosque ran out to help victims at Aldgate East and Aldgate Tube stations, setting up reception areas in the LMC and offering both facilities and volunteers to the nearby hospital.

Now tension laces the humid city air. Whitechapel station is quiet. Echoes ring out on the old wooden steps, as you clatter up to the market. The late sun beats hard on the dirty pavement, driving City workers into nearby bars. The Royal London Hospital, where so many bomb victims were treated (and Elephant Man John Merrick once stayed), stands massively above. Elderly Bangladeshi women in niqab veils wade past, balancing improbably large bags of shopping. It is a scene hundreds of years old. But the haggling is muted, the stallholders packing up early for the day.

Walking past ancient buildings which seem to lean inwards in the summer heat, you enter Altab Ali park. Once "Itchy Park", where tramps would scratch themselves on the railings, it is usually crowded with sun-seekers and drinkers. Today it is empty. You ponder the changes and you ponder the past: it was here that a young Bangladeshi man was murdered by white racists over 20 years ago. Things have changed since then: the far-right British National Party (BNP) has been seen off from its east London heartlands and the Bangladeshis are ascendant – for now. This is an Islamic community living on the cusp of Europe's most powerful financial centre.

Yet poverty and disease stalk its estates. Drugs are taking hold amongst a nominally Muslim youth. Unemployment and overcrowding are high. Tags for gangs such as the Brick Lane Massive and Stepney Terror Posse are etched across its walkways.

This is not the first time the area has known sorrow. On the trail of its well-documented miseries have traipsed some of the world's finest writers and their creations: from Charles Dicken's Fagin (based on an infamous Jewish 'fence') to Sax Rohmer's Fu Manchu; from Oscar Wilde's opium-smoking Dorian Gray to Monica Ali's Nazneen in Brick Lane.

Huguenot weavers, Irish dockers, Chinese lascars, Maltese pimps and Jewish refugees – the East End has always been the first port of call to these shores. Stalin and Trotsky once mingled in what George Orwell called "the monster doss house", Tower House in Fieldgate Street, now being converted into luxury City apartments. These streets have been home to suffragettes and anarchists, birthed municipal socialism and after the War hosted England's only Communist MP (a mantle now taken up by its new representative, the maverick Scots anti-war politician George Galloway).

Gentrification gathers apace: Robert De Niro and Cher have apartments in the redeveloped Docklands. The restored Huguenot dwellings on the streets spanning 'The Lane' are populated by best-selling writers and artists. Forty nightclubs line the once-forbidding alleyways of Shoreditch. The old Jago, a notorious Victorian 'rookery' where policemen once feared to tread, sinks beneath Spitalfields' regeneration. The local borough now has the highest national average salary in the country, thanks to the financial presence of Canary Wharf on the Isle of Dogs.

But among the Muslim Bangladeshis, there is fear. Fear of reprisals and backlash. "The tension is so high around here you can almost feel it after the bombings," says Salman, a Bangladeshi youth, as we sip sweet tea in Café Casablanca, opposite the 500-year-old Whitechapel Bell Foundry. "Probably some big nasty war will kick off with the BNP as they ain't making the situation easier."

But there is anger too. "I was asleep when it happened," gestures Hassan with a shrug, a young man originally from Somaliland, as we walk along Cable Street (scene of a famous battle between fascists and Jews & communists in 1936). "All I can say is why did we go to war? There are a lot of angry people out there. You can't really blame them, just the Government – i.e. Mr Bliar." He sucks between his teeth in disgust.

Back in Whitechapel, my friend Siraj, a long-time community worker and 'Hajji' (one who has completed the pilgrimage to Mecca) says he's just "very sad" at how it's all turned out. He's angry at extremists threatening years of painstaking work tackling social exclusion, poverty, employment, community cohesion and drugs. Churches, mosques and trade unions have long-united here in a unique alliance to fight low pay and injustice amongst the most vulnerable members of society.

Of course, the 'ummah' – the worldwide Muslim brotherhood and community – is felt as strongly here as anywhere. There were prayers said for Sheikh Yassin, the paraplegic spiritual head of Hammas who was assassinated by Israeli forces last year. The perceived injustices of Iraq, Afghanistan, and other areas are felt keenly. There are at times disturbing levels of anti-Semitism, overheard in conversations about Israel and the Jews, in the casual talk of 'kufr' (disbelievers).

During recent general elections, the streets and sidewalks surrounding Banglatown's imposing East London Mosque were plastered with extremist flyposters exhorting Muslims not to vote. Threatening eternal hellfire and damnation for those that did, there were physical clashes among Bangladeshis as a result. The battles seemed merely an extension of those taking place a hundred years earlier.

But Islam here has been used as a healing force: it has rescued gang members from a life of violence. It has brought faith to imprisoned drug dealers, young men who once wrought ruin among their own communities. There are interfaith forums too: dialogue between Jew and Christian, Muslim and Jew. There are even young Jews returning to their historic heartlands. The mosque's chairman, Dr Muhammad Bari, a lean, neatly-dressed man who is also deputy secretary of the Muslim Council of Britain, told me from inside his sweltering, whitewashed office: "Although we feel differently about the injustices on Palestine, in Islam we are asked to live peacefully with our neighbours. We're all people of The Book." I had been hearing him on the radio and TV recently. Each time he condemned the bombs unreservedly, though now he too was worried about a backlash.

Dr Bari was one of those who organised a series of peace buses to take local Muslims to a huge Trafalgar Square peace vigil. "There's shock, fear and total disgust," gang worker Abjol tells me now, as we struggle with our shoes at the mosque entrance. "At first, we were hoping it wasn't Muslims. In London, here in the East End, the community is solid. It's not like those northern cities," he says, referring to race riots in the summer of 2001 between working class white and Pakistani youths.

He sighs, before heading off to perform wudu (ritual ablution): "People are going to start talking about losing freedoms, soon. We'll be looking at a police state."